Land-based wireless communications system having a scanned directional antenna

ABSTRACT

A radio communication system is disclosed which comprises a base station for transmitting and receiving signals to and from one or more remote stations. The base station is provided with at least one receive antenna coupled to a base station receiver. The receive antenna is provided with a directional pattern in a horizontal plane and a mechanism for steering the directional pattern azimuthly, until such time as a synchronization signal transmitted by a remote station located within the coverage area is received by the base station receiver. Upon detection of the synchronization signal, scanning of the receive antenna&#39;s pattern is stopped until such time as message information can be obtained from the remote station and forwarded to a particular destination requested by the remote station. Upon receiving the information, the base station will resume scanning of the antenna, and the information will be forwarded to its requested destination.

FIELD OF THE INVENTION

The present invention is directed to a wireless communication systemhaving a base station which transmits and receives signals to and fromone or more remote stations. More specifically, the present invention isdirected to a wireless communication system having an enhanced basestation receive capability.

DISCUSSION OF BACKGROUND INFORMATION

Conventional two-way wireless communication systems typically comprise anetwork of base stations which transmit and receive signals to and fromremote stations, which are, e.g., mobile or portable. The base stationsare provided with fixed gain, fixed pattern antennas which are coupledto radio transceivers. Each base station serves a particular coveragearea, and facilitates communication of information with remote stationswhich are located within the coverage area. Since the remote stationsare typically limited in size, and because they are wireless, thushaving a limited range within which they can transmit and receivesignals, the base stations are provided to "bridge" the communicationgap between each remote station and other stations which are outside thetransmit and receive range of the remote station. While the remotestation has a limited transmit and receive range, the base station has avirtually unlimited capability to relay information to almost anylocation via, e.g., a permanently wired network such as, e.g., a publicswitched telephone network.

The transmitter power levels and antenna gains of the base and remotestations are selected so that information transmitted from each remotestation will be received by the associated base station, and so thatinformation transmitted by the base station will be received by eachremote station located within the coverage area of the base station.

In order to accommodate a large subscriber area within which remotestations can freely communicate, all portions of the total subscriberarea must be within range of a base station. Accordingly, a sufficientnumber of base stations are arranged so that their respective coverageareas (sometimes referred to as "cells") together will cover allportions of the subscriber area. In order to minimize the number of basestations needed to accommodate a given subscriber area, the base stationtransmitter power level (and associated antenna gain) should bemaximized (subject to practical and regulatory limitations) so that anyremote station located within the coverage area of that base station canaccurately receive signals transmitted from the base station. Inaddition, the receive gain of each base station antenna should bemaximized in order to increase the probability that signals transmittedby remote stations located within the coverage area will be received bythe base station.

Wireless personal communication systems, such as cellular telephonesystems, answer back paging systems, wireless data networks, specializedmobile radio networks (SMR), and rural radio telephone systems (RRTS),utilize portable remote station terminals which depend primarily onbattery technology as the primary source of electrical power. Althoughhigh energy density batteries and low power electronics have broughtabout a reduction in the size and weight of conventional portablecommunications terminals, batteries still comprise the bulk of thevolume and weight of typical portable terminals. Modern cellular, pagingand home cordless portable remote terminals have been found to attributeover 17% of their volume to just the battery supply. Accordingly,battery life and remote station terminal size are significant factorswhich dictate the system architectures of emerging communicationssystems such as personal communications networks (PCNs) and wirelesslocal loop access systems.

For these reasons, in order to minimize the weight and size of theportable terminals (so that the terminals can be "portable"), pagingsystems are usually provided with only a one-way (base station to remotestation) communications capability. In addition, cellular telephonesystems typically deploy a large number of relatively low power basestations throughout the portable service area, so that small sizeportables which have limited transmit power can communicate with thenetwork via a nearby low power base station. Such a cellular networkconfiguration is referred to as a "microcellular network."

As noted above, the paging system, in order to reduce the size ofportable terminals, will be provided with only a one-way communicationscapability, while the microcellular system is provided with an increasednumber of base stations. As a result, the paging system has reducedcapabilities, and the microcellular telephone system is more expensive.

In order to increase the potential receive range of base stations, someconventional land-based mobile radio systems are provided with fixeddirectional antennas having a large beam width in the horizontalazimuthal plane. Typical commercially available antennas include, e.g.,stationary directional antennas having a fixed 60° half-power beam widthin the azimuthal plane and +16 dB of gain. Much of the gain is achievedby arranging multiple antennas horizontally and focusing the beam bynarrowing the beam width in the elevation plane. Elevation beam widthsnarrower than about 6° are normally avoided to prevent overshooting ofthe desired coverage area due to antenna mounting inaccuracies and towersway.

Definitions

For purposes of clarification, and to assist readers in understandingthe present invention, the following terms are defined:

DIRECTIONAL ANTENNA PATTERN--A graphical representation of the radiationor reception of an antenna as a function of the direction at which theantenna is facing.

AZIMUTH--The direction of a distant point from an origination point(point of reference), expressed as the angle in the horizontal planebetween a reference line and the horizontal projection of a line joiningthe two points.

SUMMARY OF THE INVENTION

In view of the above, the present invention, through one or more of itsvarious aspects and/or embodiments, is thus presented to bring about oneor more objects and advantages, such as those noted below.

Accordingly, it is an object of the present invention to provide aland-based wireless mobile communication system which includes basestations that can detect low level signals. By providing the basestations with the capability to detect weak signals, the coverage areaof the base station can be maximized, and/or the transmission power ofthe remote station terminals can be minimized.

Another object of the present invention, in accordance with a particularaspect thereof, is to reduce the strength of signals transmitted fromremote stations to the base station, which would thus allow the batterylife of the remote terminal to be extended and/or the battery weight andsize requirements to be significantly reduced.

A yet further object of the present invention is to provide a wirelessmobile communications system having one or more base stations eachhaving a receive antenna with a steerable, narrow beam width, high gainantenna pattern. Accordingly, there will be less interference betweenbase stations due to the use of directional narrow beam antennas. Inaddition, a more efficient use of the frequency spectrum can be effectedby synchronizing the scanning of the antennas of adjacent base stations(which use the same frequency carriers).

It is yet a further object of the present invention to reduce multi-patheffects and fading, and thus to minimize performance degradation due tosuch effects, by enhancing the receive capability of the base stationsof the land-based wireless mobile communications system.

The present invention, therefore, is directed to a radio communicationssystem and a method for communicating, in which a receiving antenna of abase station, which has a directional pattern in a horizontal plane, isscanned azimuthly. In accordance with the radio communications system, abase station is provided for transmitting and receiving signals to andfrom one or more remote stations. The base station includes at least onereceive antenna coupled to a base station receiver. A device is providedfor filtering a signal received at the least one receive antenna, and afurther device is provided for processing the received signal afterfiltering by the filtering device. A control mechanism is provided forcontrolling the scanning of the directional pattern of the receivedantenna.

In accordance with a particular aspect of the radio communicationssystem of the present invention, an additional device is provided formonitoring the signal strength of the received signal, and the scanningcontrol mechanism is provided with a device for controlling scanning ofthe directional pattern as a function of the signal strength of thereceived signal. In this regard, the controlling mechanism may beprovided with a device for instructing the scanning device to stopscanning the directional pattern when the signal strength of thereceived signal is above a predetermined threshold value.

In accordance with a further aspect of the present invention, the systemincludes the one or more remote stations. Selected ones of the remotestations each comprise a device for transmitting an identifying signalpattern and message information within a frequency band monitored by thebase station receiver. The transmitting device may be provided with adevice for phrasing the message information to include an originationaddress, a destination address, a message, and error correctioninformation, so that all of the message information is transmittedsubsequent to transmission of the identifying signal pattern. Inaddition, the processing device may include a device for decodinginformation which is included in the received signal and a device formonitoring a signal strength of the received signal. In this regard, thecontrol device may include a device for determining if a received signallevel, which is determined by the monitoring device, is greater than apredetermined threshold value, and the control device may also include adevice for controlling the scanning device to move the directionalpattern to a next azimuthal position if the receive signal level is notgreater than the predetermined threshold value.

The threshold value may comprise a signal level which is substantiallyhigher than an expected background noise level. The decoding device caninclude a device for decoding the identifying signal pattern, and thesystem may be further provided with a device for determining if theidentifying signal pattern has been correctly decoded. In addition, thesystem may be provided with a device for decoding remaining portions ofthe received signal and forwarding a corresponding message to a network,if it is determined by the determining device that the identifyingsignal pattern has been correctly decoded. In this regard, the scanningcontrol device will be provided with a further device for controllingthe scanning device to move the directional pattern to a next azimuthalposition if the identifying signal pattern has not been correctlydecoded.

In accordance with a further aspect of the radio communications systemof the present invention, the antenna includes an array of collineardipole antennas.

The radio communications system may comprise a microcellularcommunications network, a wireless data network, or an answer-backpaging system.

In addition, the radio communications system of the present inventionmay be provided with a network control center connected to the basestation and a telecommunications switching network. Each of the remotestations may comprise a transmitter which transmits signals having aneffective isotropic radiated power of less than 4 watts. Moreparticularly, each of the remote stations may include a transmitterwhich transmits signals having an effective isotropic radiated power ofless than 2 watts. In addition, the directional pattern of the basestation can include a half power beam width in the azimuthal plane ofless than 30 degrees and in the elevation plane of less than 30 degrees.More particularly, the directional pattern may comprise a half powerbeam width in the azimuthal plane of less than 6 degrees and in theelevation plane of less than 8 degrees.

In accordance with a further aspect of the radio communications systemof the present invention, the at least one receive antenna of the basestation comprises a plurality of distinct antennas, and each of thedistinct antennas comprise a directional beam which can be scannedazimuthly across a range equal to a fraction of 360 degrees. Thedistinct antennas are arranged so that the total area scanned by thedistinct antennas equals 360 degrees.

In accordance with yet a further aspect of the present invention, theradio communications system further comprises a plurality of basestations. A portion of the plurality of base stations include receiversand corresponding scanned base station receive antennas which share acommon frequency channel. The system further comprises a device forsynchronizing the scanning of the base station receive antennas whichshare a common frequency channel.

Each of the remote stations may include an omnidirectional antennacoupled to a transmitter and a receiver, for transmitting and receivingsignals to and from the base station. The base station may also beprovided an omnidirectional transmit antenna.

In accordance with an alternative aspect of the radio communicationssystem of the present invention, a base station is provided forreceiving signals from one or more remote stations. The base stationincludes at least one receive antenna coupled to a base stationreceiver. The receive antenna has a directional pattern in a horizontalplane and a device for scanning the directional pattern azimuthly. Abase station may also be provided with a capability of transmittingsignals to one or more remote stations.

In accordance with the method for communicating of the presentinvention, a base station is operated to transmit and receive signals toand from one or more remote stations. The operating includes azimuthlyscanning at least one receive antenna coupled to a receiver of the basestation, wherein the receive antenna has a directional pattern in ahorizontal plane. A signal received at the at least one receive antennais filtered, the received signal is processed after filtering, and thescanning is controlled. The method may further include monitoring thesignal strength of the received signal, and controlling scanning of thedirectional pattern as a function of the signal strength of the receivedsignal.

In accordance with a further aspect of the present invention, thecontrolling includes instructing a scanning device to stop scanning thedirectional pattern when the signal strength of the received signal isabove a predetermined threshold value. Selected ones of the remotestations may be operated to transmit an identifying signal pattern andmessage information within a frequency band monitored by the basestation receiver. In this regard, the method may further compriseoperating the selected ones of the remote stations to phrase the messageinformation to include an origination address, a destination address, amessage, and error correction information, so that all of the messageinformation is transmitted subsequent to transmission of the identifyingsignal pattern. The processing may comprise decoding information whichis included in the received signal and monitoring a signal strength ofthe received signal. Moreover, the method may include steps such asdetermining if a received signal level, which is determined during themonitoring, is greater than a predetermined threshold value, andcontrolling the scanning to move the directional pattern to a nextazimuthal position if the received signal level is not greater than thepredetermined threshold value. The predetermined threshold value mayinclude a signal level which is substantially higher than an expectedbackground noise level.

The decoding may include decoding the identifying signal pattern, andthe method may be further provided with steps such as determining if theidentifying signal pattern has been correctly decoded, decodingremaining portions of the received signal and forwarding a correspondingmessage to a network, if it is determined that the identifying signalpattern has been correctly decoded. In addition, the method may includecontrolling the scanning to move the directional pattern to a nextazimuthal position if the identifying signal pattern has not beencorrectly decoded.

The antenna may comprise an array of collinear dipole antennas.

The method of the present invention may utilize a microcellularcommunications network, a wireless data network, or an answer backpaging system.

A network control center may be operated which is connected to the basestation and a telecommunications switching network. Each of the remotestations may comprise a transmitter which transmits signals having aneffective isotropic radiated power of less than 4 watts, and moreparticularly having an effective isotropic radiated power of less than 2watts. In addition, the directional pattern may include a half powerbeam width in the azimuthal plane of less than 30 degrees and in theelevation plane of less than 30 degrees, and more particularly, a halfpower beam width in the azimuthal plane of less than 6 degrees and inthe elevation plane of less than 8 degrees.

The at least one receive antenna may include a plurality of distinctantennas, and the communicating method may further comprise scanning adirectional beam of each of the distinct antennas azimuthly across arange equal to a fraction of 360 degrees, the individual antennas beingarranged so that the total area scanned by the distinct antennas equals360 degrees.

The method may further include operating a plurality of base stations, aportion of the plurality of base stations comprising receivers andcorresponding scanned base station receive antennas which share a commonfrequency channel, and synchronizing the scanning of the base stationreceive antennas which share a common frequency channel. Each of theremote stations may include an omnidirectional antenna coupled to atransmitter and a receiver, for transmitting and receiving signals toand from the base station, and the base station may comprise anomnidirectional transmit antenna.

The above-listed and other objects, features, and advantages of thepresent invention will be more fully set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further described in the detailed descriptionwhich follows, by reference to the noted plurality of drawings by way ofnon-limiting examples of preferred embodiments of the present invention,in which like reference numerals represent similar parts throughout theseveral views of the drawings, and wherein:

FIG. 1A illustrates a land-based wireless mobile communication system inaccordance with a particular embodiment of the present invention;

FIG. 1B illustrates a base station utilized in the mobile communicationssystem shown in FIG. 1A;

FIG. 2 illustrates a block diagram of a base station receive system ofthe land-based wireless mobile communication system shown in FIG. 1A;

FIG. 3 illustrates a block diagram of the transmit message structure ofa remote station transmitter to be implemented with the land-basedwireless mobile communication system of FIG. 1A;

FIG. 4 illustrates, in a flow chart, the logical flow of a dataprocessing device implemented in the base station receive system shownin FIG. 2;

FIG. 5 illustrates a particular embodiment of a base station receiveantenna coupled to an exemplary RF signal processing device;

FIG. 6 illustrates an antenna pattern of a single array element of thebase station receive antenna array which is shown in FIG. 2;

FIG. 7 illustrates a second embodiment base station receive antennaarray which can be implemented in the land-based wireless mobilecommunication system of the present invention; and

FIG. 8 illustrates, in a flow diagram, the operation of a networkcontrol center in accordance with a particular embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in greater detail, FIG. 1A is an overallperspective view of a land-based wireless mobile communication system 10in accordance with the present invention. A plurality of base stations12 are coupled to a telecommunications switching network 20, which maycomprise, e.g., a PSTN (Public Switched Telephone Network), or a packetnetwork. Each base station 12 includes a steerable base station receiveantenna 14; the direction of the antenna beam of each antenna 14 isindicated by an antenna beam direction indicating symbol 22. A pluralityof remote stations 16, which are compatible with the wirelesscommunications system 10, may be dispersed throughout a coverage area(e.g., cell) 19 of each base station 12.

As shown in FIG. 1B, each base station 12 includes a transmit antenna 15and a receive antenna 14, which are coupled to a transmit system 21 anda receive system 13, respectively. Although the transmit and receiveantennas are illustrated in FIG. 1B as distinct, the present inventiondoes not preclude the use of a single transmit/receive antenna.

In FIG. 1B operation of the above-described communications network,information may be transmitted to a remote station 16 by either a remotestation 16, or by an auxiliary network station (e.g., a telephone) whichis connected to telecommunications switching network 20. In transmittinginformation from the telephone to a remote station 16, a call isinitiated by a communicating party, and the information is routedthrough use of the telecommunications network 20 to network controlcenter 18. The information is then forwarded to one or more appropriatebase stations 12, which in turn transmit the information to theappropriate remote station 16, which comprises, e.g., a small,lightweight portable hand-held terminal or paging receiver.

Should wireless mobile communication system 10 comprise an answer backpaging system, the remote subscriber 17 (i.e., the user of the remotestation 16) will input the information to be returned to thecommunicating party into remote station 16, which will transmit theinformation, via an omni-directional transmit antenna, to a base station12 corresponding to the coverage area 19 in which remote station 16 islocated.

Base station 12 directs the narrow beam of its corresponding basestation receive antenna 14 toward remote station 16, so that theinformation can be received by base station 12; base station 12 thenforwards the received information to NCC 18, for subsequent transmissionto the communicating party via telecommunications switching network 20.

Each base station receive antenna 14 includes a narrow, high gainreceive pattern which is scanned throughout at least a portion of thecoverage area 19 of the base station 12. In order to transmitinformation, each remote station 16 prefaces such information with asynchronization signal. Base station 12 scans the focused antenna beam(of base station receive antenna 14) azimuthly until the synchronizationsignal transmitted by a particular remote station 16 is received with asufficiently strong signal level. Upon detection of this synchronizationsignal, the antenna beam is temporarily stopped and directed toward thelocation of the remote station 16, until such time as the informationtransmitted by the remote station 16 can be fully recovered by basestation 12. Once the information transmitted by remote station 16 isreceived, base station 12 will resume scanning of the beam of basestation receive antenna 14.

In order to effect transmission from base stations 12 to remote stations16, each base station 12 may be provided with a high gainomni-directional base station transmit antenna 15 (FIG. 1B).Accordingly, by using an omni-directional transmit antenna 15, scanningwill not be necessary in order to transmit information to a particularremote station 16.

FIG. 2 illustrates, in a block diagram, the receive system 13 of a basestation 12 in accordance with a particular aspect of the presentinvention. Base station receive antenna 14 comprises an array ofcollinear antennas 24, each of which is connected to a respective inputof an RF signal processing device 26. Base station receive antenna 14 isconfigured to have a directional pattern in a horizontal plane, and RFsignal processing device 26 is provided to steer the directional patternof receive antenna 14 azimuthly. Signals which are recovered from basestation receive antenna 14 (i.e., which are located within the steereddirectional pattern) are output from RF signal processing device 26 andinput to a receiver 28.

Receiver 28 comprises an input 29a, a received signal strength indicator(RSSI) output 29b, and a received signal output 29c. Received signaloutput 29c of receiver 28 is connected directly to a decoder 30, whichis in turn connected, at an output thereof, to a data processing device32. RSSI output 29b is also connected to a data processing device 32.Data processing device 32 has an output 33 which is connected to ascanning array controller 34 which controls the RF signal processingdevice 26 to steer (i.e., scan) the antenna beam.

Each of antennas 24 is fed into RF signal processing device 26 whichcontrols the steering direction of the directional base station receiveantenna 14. RF signal processing device 26 can, optionally, beimplemented as a set of digitally controlled complex weights (e.g.,digitally controlled phase shifters) that can be adjusted to steer anarrow beam in a designated direction. Alternatively, by way of example,should individual antenna elements be provided which have sufficientgain, RF signal processing device 26 can be implemented as a set of RFswitches that are digitally controlled to switch on and off respectiveindividual antenna elements or sets of antenna elements so that a highgain, narrow beam can be steered in a designated direction by choosingthe individual antenna elements or sets of antenna elements.

In the embodiment depicted in FIG. 2, base station receive antenna 14comprises an array of collinear dipole antennas 24. However, it is notedthat any well-known antenna technique can be used to synthesize a highgain, electronically steerable antenna. For example, an array could beprovided which consists of a microstrip patch antenna array, a waveguidehorn antenna array, or an array of corner reflector antennas.

Scanning array controller 34 receives instructions from data processingdevice 32 regarding the position at which the beam of antenna 14 shouldbe steered. Scanning array controller 34 provides scanning informationto RF signal processing device 26 in an appropriate format readable byRF signal processing device 26, and (optionally) regulates the powerinput to elements within RF signal processing device 26. By way ofexample, the appropriate settings of RF signal processing device 26 maybe set by a scanning array controller 34 which consists of a standarddigital interface such as a Phase Shifter Interface Electronics (PIE)board which is commercially available from Electromagnetic Sciences,Inc., to be described in further detail below. However, any appropriatedrive circuitry, such as, e.g., an analog interface, may be used.

Radio frequency signals that are received by base station receiveantenna 14 are forwarded from base station receive antenna 14, via RFsignal processing device 26, to an input 29a of receiver 28. Receiver 28may comprise, e.g., a standard, commercially available radio receiverwhich extracts desired radio signals and removes undesired signals fromthose received by base station receive antenna 14. Receiver 28demodulates any information impressed on an RF carrier of interest, andpasses the demodulated signal, via an output 29c, to decoder 30. Inaddition, in accordance with the embodiment shown in FIG. 2, receiver 28sends a Received Signal Strength Indication (RSSI) to data processingdevice 32, via an RSSI output 29b. The RSSI is provided as an indicatorof the reliability and quality of the received signal, and can be usedto aid data processing device 32 in determining the positioning of thebeam heading of base station receive antenna 14.

Decoder 30 accepts the demodulated signal output from received signaloutput 29c of receiver 28, and conditions it to be compatible with dataprocessing device 32. In the embodiment shown in FIG. 2, decoder 30converts an analog demodulated signal into a digital format. Decoder 30may comprise the necessary components, for example, to detect digitalsignals and analog signals (such as voice signals). In addition, inaccordance with a particular embodiment of the present invention,decoder 30 may be provided with the necessary components to interpretportions of the demodulated signal. For example, decoder 30 maydetermine if a synchronization signal is present in a received signal,and inform data processing device 32 that a synchronization signal ispresent. Decoder 30 may also be provided with circuitry to detect andcorrect error patterns that may occur in the demodulated signal viastandard correction techniques.

Data processing device 32 provides the overall decision intelligence forbase station receive system 13. In the present embodiment, dataprocessing device 32 is implemented using standard stored programcontrol microprocessor techniques. Data processing device 32 instructsscanning array controller 34 to send appropriate instructions toposition the antenna beam of base station receive antenna 14 to aspecific azimuthal heading. Based on the RSSI and decoder signals, dataprocessing device 32 determines the position at which the antenna beamshould be placed. If the RSSI and decoder signals are such that a validmessage is expected to be reliably received at a given heading ofantenna 14, data processing device 32 will cause the antenna 14 to dwellat a particular azimuthal position and wait for a sufficiently longperiod of time to receive information from the remote station 16 ofinterest, which may include information such as RemoteStation-identification, a destination address, and a message to beforwarded to a third party. Data processing device 32 also makes adetermination as to whether the received information is reliable.

Each base station 12 (FIG. 1A) is provided with a base station transmitsystem 21 (FIG. 1B) in addition to base station receive system 13, shownin FIG. 2. Base station transmit system 21 can be implemented usingconventional methods. Because adequate transmit power can be easilygenerated by the base station, since there are no limitations as to sizeand weight of the same, no scanning antenna is necessary to amplify orincrease the range of the transmit antenna. It is noted that in certainapplications (such as for fixed point-to-multi-point communications) itmay be desirable to provide the base station transmit system with ascanning antenna system such as that utilized in the base stationreceive system 13 shown in FIG. 2.

Each remote station 16 of land-based wireless mobile communicationssystem 10 (FIG. 1A) can be implemented using standard transceivertechnology, and should be provided with a transmit message structurewhich allows the nearby base station 12 to position the scanning antenna14 so that signals transmitted by remote station 16 can be received bybase station 12.

FIG. 3 illustrates one embodiment of transmit message structure 44 ofremote stations 16. Transmit message structure 44 of remote station 16can include a message sync word 46, an origination address 48, adestination address 50, a message 52, and an error correction sequence54, each placed consecutively in time. Transmit message structure 44 caninclude, for example, a binary sequence having desired correlationproperties, such as a Barker sequence. The origination address can berepresented by a binary encoded identification sequence for identifyingthe remote station. The destination address can be represented by abinary encoded sequence which identifies the recipient of the message.The encoded message can be represented in binary encoded form, andincludes, e.g., information that a subscriber 17 utilizing remotestation 16 desires to send to another party. Standard error correctionand detection techniques can be used to improve the reliability of themessages received. Reliability may be further enhanced when more thanone base station 12 can receive signals transmitted by a remote station16. This is due to a phenomenon known as macrodiversity.

With respect to the communications protocol of the overallcommunications system 10, an answer back paging system may beimplemented having a protocol such as disclosed in publishedinternational patent application WO 89/08369, the content of which isexpressly incorporated by reference herein in its entirety.

Network control center (NCC) 18 interfaces the land-based wirelessmobile communication system 10 to an appropriate telecommunicationsswitching network 20, such as, e.g., a public switch telephone network(PSTN), a packet data network, or another wireless network, etc. NCC 18can be configured to provide additional capabilities such as positiontriangulation, elimination of duplicate messages, and selection of thebest quality messages.

FIG. 8 illustrates, in a flow diagram, the operation of NCC 18 inaccordance with a particular embodiment of the present invention. Instep S7, NCC 18 receives all messages from base stations 12 which havebeen received and processed without error. Subsequently, in step S8, NCC18 determines whether duplicate messages exist. If so, in step S9, NCC18 eliminates duplicate messages by selecting the one message that isestimated to be of the best quality for subsequent routing to thedestination. In step S10, the position of the remote station, from whichthe message has been sent, is estimated by triangulation. Subsequently,in step S11, the position information is appended to the messageinformation, and in step S12, the message information is routed to itsdestination via switching network 20.

The position information can be utilized by a recipient of the messageinformation as a need for the same arises. For example, should it bedesirable to track the location of a plurality of remote stations, therecipient of the message information can do so by appropriately decodingand processing the position information which is forwarded.

Should NCC 18 determine at step S8 that no duplicate messages exist, NCCwill skip steps S9-S11, and proceed to route the message information toits destination at step S12.

It is noted that the message information may also include informationfor controlling NCC 18 itself. Such information could be used, forexample, to provide a "key" (i.e., access code) needed to access thesystem, to indicate status information, to communicate with a systemoperated by another group, etc. NCC 18 may also be configured to collectstatistics regarding system usage.

The operation of data processing device 32 will now be described infurther detail while referring to the flow chart depicted in FIG. 4. Instep S1, data processing device 32 instructs scanning array control 34to cause antenna array 14 to scan to a next azimuthal position.Subsequently, in step S2, a determination is made as to whether a signallevel received by receiver 28 (while antenna 14 is at the specifiedazimuthal position) is greater than a predetermined threshold value. Ifthe signal is not greater than the threshold value, the process returnsto step S1 and the antenna is scanned to a next azimuthal position. Onthe other hand, if the signal is determined to be greater than thethreshold value at step S2, data processing device 32 proceeds to stepS3 where a determination is made as to whether a sync code word has beendetected, correctly decoded by decoder 30, and appropriately forwardedto data processing device 32. If such a sync code word has not beenappropriately forwarded to data processing device 32, data processingdevice 32 proceeds to step S4, and a record is made (in an appropriatememory device [not shown]) that the particular azimuth position hasinterference. The process subsequently returns to step S1, to scan anext azimuthal position. If the sync code word is determined at step S3to be properly forwarded and correct, data processing device 32 proceedsto step S5, and the remaining message information is decoded.Subsequently, in step S6, the message information is accepted by dataprocessing device 32 and routed to network control center 18, which willappropriately route the message to the destination indicated by remotestation 16. Subsequent to passing the message to network control center18 at step S6, data processing device 32 will return to step S1.

The control process which is executed by data processing 32, asillustrated in FIG. 4, is not shown to include a switch for initiatingor ending execution thereof. However, for any one of a number ofreasons, such as to stop the system for maintenance purposes, such aswitch may be provided.

By execution of the steps indicated in FIG. 4, a high gain, narrowazimuthal beam width antenna receive pattern is rapidly scanned over thearea to be served (coverage area) until a synchronization pattern(message sync word) is detected. The synchronization pattern istransmitted by a remote station 16 when the remote station desires tosend information to a specified destination. The synchronization pattern(in the form of a sync code word) is transmitted for a sufficientduration so that each base station within range can sweep through everyazimuthal direction at least once and detect the presence of thesynchronization pattern.

If the synchronization pattern is detected, the scanning antenna 14 isstopped and dwells at the azimuthal heading that produces the mostreliable signal from remote station 16. Remote station 16 transmits itsidentification code, the code corresponding to the destination for themessage, the message, and any error correction/detection informationsubsequent to the sync pattern. If base station 12 decodes thisinformation without error, it sends the information to network controlcenter 18 for routing to the appropriate destination. This routing canbe accomplished via, e.g., a public switch telephone network (PSTN), apacket data network, a remote station of another wireless system via alocal switch, or any other such switching network. An indication of theazimuthal beam heading may also be sent to NCC 18 from each base station12 that decodes the message properly. NCC 18, in addition to receivingthe messages, can also triangulate the position of each remote station16 (if possible), and route a single copy of the message and remotestation location to its destination.

FIG. 5 illustrates an exemplary embodiment of base station receiveantenna 14 and RF signal processing device 26. Base station receivingantenna 14 comprises a plurality (1-N) of collinear dipole antennas 24arranged in a parallel fashion in a plane which is parallel to anantenna ground plane 36. Each collinear dipole antenna 24 is placed lessthan one-half wavelength from an adjacent collinear dipole antenna 24.In the specific embodiments illustrated herein, the antenna will scanonly in the azimuth plane. However, the antenna may be designed to alsoscan in the elevation plane.

Each terminal 59 of each antenna 24 is connected to a beam steeringprocessing device 65. Beam steering processing device 65 is configuredto steer the signal receiving beam of base station receive antenna 14by, e.g., adjusting the phase or time of arrival of each signal receivedfrom each individual collinear dipole antenna 24. In order to adjust thephase or time of arrival of each signal, device 65 may be provided with,e.g., ferrite phase shifters, Time Delay Units (TDUs), PIN diode phaseshifters, or commutated switchable lenses. In addition, beam steeringprocessing device 65 is provided with a device for combining the signalsreceived from the individual collinear dipole antennas 24. Beam steeringprocessing device 65 may also be provided with bandpass filters, andamplifying devices, in any desired and effective order and combination.

Thus, in one non-limiting alternative, beam steering device 65 couldcomprise ferrite phase shifters in combination with appropriate bandpassfilters and amplifiers, and one or more combiners, such that the systemwill be able to provide for beam steering, bandpass filtering, andcombining of signals received by the array of antennas 24.

The output of beam steering processing device 65 is connected to abandpass filter 68 which is connected in cascade to an isolator 70.Isolator 70 prevents signals from propagating back toward antenna 14.The output of isolator 70 is connected to a multiplier 72 (mixer), atwhich the signal output by isolator 70 is multiplied by a modulatingsignal from an oscillator 78. The modulating signal is filtered by abandpass filter 74 and input to a second input terminal of multiplier72. The resulting multiplied signal is input to a low pass filter 76 toremove high frequency signal components which are outside the range ofreceiver 28, and the output of low pass filter 76 is connected toreceiver 28.

Each of the elements depicted in FIG. 5 may be implemented withcommercially available components. As a non-limiting illustrativeexample, beam steering processing device 65 may be configured to includeElectromagnetic Sciences 6-bit ferrite phase shifters, model 630-1,which are commercially available from Electromagnetic Sciences.

Isolator 70 prevents signals from propagating in a direction opposite tothat intended (i.e., in a direction toward antenna 14), so thatreflected signals are not transmitted. Oscillator 78, bandpass filter74, multiplier 72 and low pass filter 76 together comprise a frequencydown converter for shifting the signals received by antennas 24 to afrequency range of receiver 28.

The low noise frequency downconverter is used to translate the signalsto a frequency range tunable within an existing general coverage ofreceiver 28, and may be configured to set the system noise figure.

FIG. 6 illustrates a possible antenna element receive pattern 80 of anindividual collinear dipole antenna 24 in an array environment. Thesolid line represents a calculated array element pattern, and the dottedline represents a theoretical cosine (azimuthal angle) pattern. The farfield pattern for the array antenna has a cosine(x)/x pattern atbroadside.

Referring back to FIG. 5, it is noted that a particular implementationof the antenna illustrated in FIG. 5 can include, as an illustrativeexample, the following features: For receiving microwave signals in afrequency band such as 2.4 GHz, the antenna can be configured to have a3 dB (1/2 power) beam width of about 5.7° in the elevation plane andabout 7.7° in the azimuth plane at a position broadside to the antenna.The directivity (i.e., the value of directive gain in a direction ofmaximum value) of the antenna may be about 28.6 dB with respect to anisotropic radiator. The antenna may be designed to have a first sidelobe which is about 13 dB down from the principal pattern lobe atbroadside, and can be configured to scan about + or -60° in the azimuthplane (0° being at the antenna broadside) without significantintroduction of a grating lobe or splitting of the main beam. In theembodiment depicted, the dipole antennas 24 are separated by less thanone-half wavelength.

Should the antenna be configured to scan an azimuthal range of 120°, atotal of three systems will be required at each omnidirectionalinstallation so that a total 360° azimuthal range can be scanned. Havingthree beams simultaneously scanning the coverage region will allowcomplete omnidirectional coverage by the receive system. Such aconfiguration has an additional advantage in that a portable terminalattempting to transmit can be acquired in a third of the time that asingle omnidirectional array would require.

FIG. 7 illustrates a further embodiment of a base station receiveantenna 14' which can be connected to each of base stations 12 (FIG. 1A)of land-based wireless mobile communications system 10 (FIG. 1A). Basestation receive antenna 14' comprises an array 25 of dipole arrayelement cards 24' with each card 24' comprising an N (e.g., N=4) dipolearray element. Each card 24' is connected to a corresponding phaseshifter 64' via an appropriate connector (e.g., coaxial) 82, and a lownoise amplifier 62' is connected between an output of each variablephase shifter 64' and a combined signal terminal (which may include,e.g., a combiner [not shown]) which is input to receiver 28. Phaseshifters 64', low noise amplifiers 62' and dipole array element cards24' can be fully integrated, as shown, on one or more circuit boards.For example, these elements can be printed onto a dielectric substrate,such as, for example, glass epoxy printed circuit board material. Thisconfiguration renders the antenna assembly easily duplicated, accuratein specifications, and less expensive when mass produced. Further, asshown in FIG. 7, the phase shifters 64' may be controlled by aconventional phase shifter control 66'.

More information related to microstrip antennas, such as the onedepicted in FIG. 7, is provided by J. R. James, P. S. Hall & C. Wood ina publication entitled "Microstrip Antenna Theory and Design," PeterPeregrinus Ltd. (London), 1986, at pages 10 and 111-175, the content ofwhich is expressly incorporated by reference herein in its entirety.Additional information regarding planar phase array antennas is providedby C. A. Balanis, in "Antenna Theory, Analysis and Design," Harper andRow (New York), 1982, at pages 202-274, and by Johnson & Jasik in"Antenna Engineering Handbook," McGraw Hill (New York), 1984, at pages20-1 to 20-67. Each of these references is expressly incorporated byreference herein in its entirety.

Antenna 14 (FIG. 5) or 14' (FIG. 7) of mobile communication system 10may include a steerable antenna with a specified value of gain anddynamic beam shaping for coverage shaping or null-steering. Costreduction (among many other factors) may affect the antenna and controlcircuitry configurations to be implemented in the present invention.

The above-described elements of the present invention can be implementedwith commercially available components. For example, receiver 28 (seeFIG. 2) can be implemented with a Rhode-Schwarz ESVP receiver. Decoder30 may comprise, for example, a paging receiver decoder based on theCCIR-RPC1 standard to synchronize and decode alphanumeric messages. Inthis regard, reference is made to "Standard Codes and Formats forInternational Radio Paging," Recommendations and Reports of CCIR, 1986Vol. VIII-1, Geneva 1986, the content of which is expressly incorporatedherein in its entirety. Origination address, destination address, andmessage information will be imbedded into the CCIR-specified messagestructure. Data processing device 32 may be implemented, for example,with the use of an IBM compatible personal computer. Scanning arraycontroller 34 may comprise, for example, a Phase Shifter InterfaceElectronics (PIE) Board Interface which is manufactured byElectromagnetic Sciences, Inc., P.O. Box 7700, Norcross, Ga. 30091-7700,(404) 263-9200.

While the invention has been described with reference to preferredembodiments, it is understood that the words which have been used hereinare words of description, rather than words of limitation. Changes maybe made, within the purview of the appended claims, without departingfrom the scope and spirit of the invention in its aspects. Although theinvention has been described herein with reference to particular means,materials and embodiments, the invention is not intended to be limitedto the particulars disclosed herein; rather, the invention extends toall equivalent structures, methods, and uses, such as are within thescope of the appended claims.

What is claimed is:
 1. A radio communications system, comprising:one ormore remote stations, each of said remote stations comprising means fortransmitting an identifying signal pattern and message informationwithin a frequency band; a base station for transmitting and receivingsignals to and from said remote stations, said base station comprisingat least one receiving antenna coupled to a base station receiver whichmonitors said frequency band, said at least one receive antenna having adirectional pattern in a horizontal plane and means for scanning saiddirectional pattern azimuthally; means for filtering a signal receivedat said at least one receive antenna means for processing said receivesignal after filtering by said filtering means, said processing meanscomprising means for decoding information which is included in saidreceived signals; means for monitoring a signal strength of saidreceived signal; and means for controlling said scanning means; whereinsaid decoding means comprises means for decoding said identifying signalpattern, said system further comprising:means for determining if saididentifying signal pattern has been correctly decoded; and means fordecoding remaining portions of said received signal and forwarding acorresponding message to a network, if it is determined by saiddetermining means that said identifying signal pattern has beencorrectly decoded; said means for controlling said scanning meansfurther comprising means for instructing said scanning means to movesaid directional pattern from one azimuthal position to another if saididentifying signal pattern has not been correctly decoded.
 2. the radiocommunications system according to claim 1, wherein said means forcontrolling said scanning means comprises means for controlling scanningof said directional pattern as a function of the signal strength of saidreceived signal.
 3. The radio communications system according to claim1, wherein said transmitting means of said remote stations furthercomprises means for phrasing said message information to include anorigination address, a destination address, a message, and errorcorrection information, wherein all of said message information istransmitted subsequent to transmission of said identifying signalpattern.
 4. The radio communications system according to claim 1,wherein said means for controlling said scanning means comprises:meansfor determining if the received signal strength, determined by saidmonitoring means, is greater than said predetermined threshold value;and means for instructing said scanning means to move said directionalpattern from one azimuthal position to another if said received signalstrength is not greater than said predetermined threshold value.
 5. Theradio communications system according to claim 4, wherein said thresholdvalue comprises a signal level which is substantially higher than anexpected background noise level.
 6. The radio communications systemaccording to claim 1, wherein said at least one receive antennacomprises an array of collinear antennas.
 7. The radio communicationssystem according to claim 1, wherein said radio communications systemcomprises a microcellular communications network.
 8. The radiocommunications system according to claim 1, wherein said radiocommunications system comprises a wireless data network.
 9. The radiocommunications system according to claim 1, wherein said radiocommunications system comprises an answer back paging system.
 10. Theradio communications system according to claim 1, said system furthercomprising a network control center connected to said base station andconnected to a telecommunications switching network.
 11. The radiocommunications system according to claim 1, wherein each of said remotestations comprises a transmitter which transmits signals having aneffective isotropic radiated power of less than 4 watts.
 12. The radiocommunications system according to claim 1, wherein each of said remotestations comprises a transmitter which transmits signals having aneffective isotropic radiated power of less than 2 watts.
 13. The radiocommunications system according to claim 1, wherein said directionalpattern comprises a half power beam width in the azimuthal plane of lessthan 30 degrees and a half power beam width in the elevation plane ofless than 30 degrees.
 14. The radio communications system according toclaim 1, wherein said directional pattern comprises a half power beamwidth in the azimuthal plane of less than 6 degrees and a half powerbeam width in the elevation plane of less than 8 degrees.
 15. The radiocommunications system according to claim 1, wherein said at least onereceive antenna comprises a plurality of distinct antennas, each of saiddistinct antennas comprising means for scanning a directional beamazimuthly across a range equal to a fraction of 360 degrees, saiddistinct antennas being arranged so that the total area scanned by saiddistinct antennas equals 360 degrees.
 16. The radio communicationssystem according to claim 1, further comprising a plurality of basestations, a portion of said plurality of base stations comprisingreceivers and corresponding scanned base station receive antennas whichshare a common frequency channel, and means for synchronizing thescanning of said base station receive antennas which share said commonfrequency channel.
 17. The radio communications system according toclaim 1, wherein each of said remote stations comprises anomnidirectional antenna coupled to a transmitter and a receiver, fortransmitting and receiving signals to and from said base station. 18.The radio communications system according to claim 1, wherein said basestation comprises an omnidirectional transmit antenna.
 19. The radiocommunications system according to claim 1, wherein said instructingmeans instructs said scanning means to continuously scan saiddirectional pattern azimuthally until the signal strength of saidreceived signal is detected to be above said predetermined thresholdvalue.
 20. The radio communications system according to claim 1, whereinselected ones of said remote stations comprise means for transmitting amessage structure that includes an identifying signal pattern, and saidprocessing means comprises means for decoding said identifying signalpattern, said instructing means instructing said scanning means toresume scanning of said directional pattern, even after the signalstrength of said received signal is detected to be above saidpredetermined threshold value, if said identifying signal pattern hasnot been correctly decoded by said decoding means.
 21. A method forcommunicating, comprising:operating a base station to transmit andreceive signals to and from one or more remote stations, said methodcomprising azimuthally scanning at least one receive antenna coupled toa receiver of the base station, wherein said at least one receiveantenna has a directional pattern in a horizontal plane; operatingselected ones of said remote stations to transmit an identifying signalpattern and message information within a frequency band monitored bysaid base station receiver; filtering a signal received at said at leastone receive antenna; processing said received signal after filtering,said processing comprising decoding information which is included insaid received signal; monitoring the signal strength of said receivedsignal; and controlling said scanning; wherein said decoding comprisesdecoding said identifying signal pattern, said method furthercomprising:determining if said identifying signal pattern has beencorrectly decoded; decoding remaining portions of said received signaland forwarding a corresponding message to a network, if it isdetermined, during said determining, that said identifying signalpattern has been correctly decoded; and controlling said scanning tomove said directional pattern from one azimuthal position to another ifsaid identifying signal pattern has not been correctly decoded.
 22. Themethod for communicating according to claim 21, further comprisingcontrolling scanning of said directional pattern as a function of thesignal strength of said received signal.
 23. The method forcommunicating according to claim 21, further comprising operating saidselected ones of said remote stations to phrase said message informationto include an origination address, a destination address, a message, anderror correction information, so that all of said message information istransmitted subsequent to transmission of said identifying signalpattern.
 24. The method for communicating according to claim 21, furthercomprising:determining if the received signal strength is greater thansaid predetermined threshold value; and controlling said scanning tomove said directional pattern from one azimuthal position to another ifsaid received signal strength is not greater than said predeterminedthreshold value.
 25. The method for communicating according to claim 24,wherein said predetermined threshold value comprises a signal levelwhich is substantially higher than an expected background noise level.26. The method for communicating according to claim 21, wherein said atleast one receive antenna comprises an array of collinear antennas. 27.The method for communicating according to claim 21, wherein said methodutilizes a microcellular communications network.
 28. The method forcommunicating according to claim 21, wherein said method utilizes awireless data network.
 29. The method for communicating according toclaim 21, wherein said method utilizes an answer back paging system. 30.The method for communicating according to claim 21, further comprisingoperating a network control center which is connected to said basestation and is connected to a telecommunications switching network. 31.The method for communicating according to claim 21, wherein each of saidremote stations comprises a transmitter which transmits signals havingan effective isotropic radiated power of less than 4 watts.
 32. Themethod for communicating according to claim 21, wherein each of saidremote stations comprises a transmitter which transmits signals havingan effective isotropic radiated power of less than 2 watts.
 33. Themethod for communicating according to claim 21, wherein said directionalpattern comprises a half power beam width in the azimuthal plane of lessthan 30 degrees, and a half power beam width in the elevation plane ofless than 30 degrees.
 34. The method for communicating according toclaim 21, wherein said directional pattern comprises a half power beamwidth in the azimuthal plane of less than 6 degrees, and a half powerbeam width in the elevation plane of less than 8 degrees.
 35. The methodfor communicating according to claim 21, wherein said at least onereceive antenna comprises a plurality of distinct antennas, saidscanning comprising scanning a directional beam of each of said distinctantennas azimuthly across a range equal to a fraction of 360 degrees,said distinct antennas being arranged so that the total area scanned bysaid distinct antennas equals 360 degrees.
 36. The method forcommunicating according to claim 21, further comprising:operating aplurality of base stations, a portion of said plurality of base stationscomprising receivers and corresponding scanned base station receiveantennas which share a common frequency channel; and synchronizing thescanning of said base station receive antennas which share said commonfrequency channel.
 37. The method for communicating according to claim21, wherein each of said remote stations comprises an omnidirectionalantenna coupled to a transmitter and a receiver, for transmitting andreceiving signals to and from said base station.
 38. The method forcommunicating according to claim 21, wherein said base station comprisesan omnidirectional transmit antenna.
 39. The method for communicatingaccording to claim 21, further comprising instructing said scanningmeans to continuously scan said directional pattern azimuthally untilthe signal strength of said received signal is detected to be above saidpredetermined threshold value.
 40. The method for communicatingaccording to claim 21, further comprising operating selected ones ofsaid remote stations to transmit a message structure that includes anidentifying signal pattern, wherein said processing comprises decodingsaid identifying signal pattern and said instructing comprisesinstructing said scanning means to resume scanning of said directionalpattern, even after the signal strength of said received signal isdetected to be above said predetermined threshold value, if saididentifying signal pattern has not been correctly decoded.